Problem: $ { \left[\begin{array}{r}{2} \\ {1} \\ {1}\end{array}\right]+\left[\begin{array}{r}{-1} \\ {3} \\ {1}\end{array}\right] = {?} } $
To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{r}{2}+{-1} \\ {1}+{3} \\ {1}+{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{1} \\ {4} \\ {2}\end{array}\right]}$